In recent years, there has been development of organic semiconducting (OSC) materials in order to produce more versatile, lower cost electronic devices. Such materials find application in a wide range of devices or apparatus, including organic field effect transistors (OFETs), organic light emitting diodes (OLEDs), organic photodetectors (OPDs), organic photovoltaic (OPV) cells, sensors, memory elements and logic circuits to name just a few. The organic semiconducting materials are typically present in the electronic device in the form of a thin layer, for example of between 50 and 300 nm thickness.
The photosensitive layer in an OPV or OPD device is typically composed of at least two materials, a p-type semiconductor such as a polymer, an oligomer or a define molecular unit and a n-type semiconductor such as a fullerene derivative, graphene, a metal oxide, or quantum dots. In recent years, many p-type semiconductors, mainly polymers, have been prepared to enhance the performance of an OPV device. In comparison, the development of n-type semiconductor has been limited to only a few selected candidates.
Novel n-type semiconductors as promising alternative to PCBM-C60 fullerene are limited. FIG. 1 shows some known fullerene derivatives, including Fullerene 1 and the respective multiple adducts both described in WO2008/018931 and WO2010/087655, Fullerene 2 and the respective multiple adducts both described in U.S. Pat. No. 8,217,260, Fullerene 3 described in JP 2012-094829, Fullerene 4 described in WO 2009/008323 and JP 2011-98906 and Fullerene 5 and the respective multiple adducts both described in JP 2011-181719. However, the physical properties of these fullerene derivatives, such as solubility, light stability, thermal stability are limiting their use in commercial applications.
Thus there is still a need for fullerene derivatives which are easy to synthesize, especially by methods suitable for mass production, show good structural organization and film-forming properties, exhibit good electronic properties, especially a high charge carrier mobility, a good processability, especially a high solubility in organic solvents, and high light and thermal stability.
It was an aim of the present invention to provide fullerene derivatives that provide one or more of the above-mentioned advantageous properties. Another aim of the invention was to extend the pool of n-type OSC materials available to the expert. Other aims of the present invention are immediately evident to the expert from the following detailed description.
The inventors of the present invention have found that one or more of the above aims can be achieved by providing cyclohexadiene fullerenes as disclosed and claimed hereinafter.
Surprisingly it was found that these cyclohexadiene fullerenes demonstrate one or more of the improved properties as described above, especially for use in OPV/OPD applications, compared to the fullerenes disclosed in prior art.
Substituted cyclohexadiene fullerenes have been proposed for medical applications, see for example S. Durdagi et al., Bioorg. Med. Chem. 2008, 16, 9957-9974 and Periya et al., Tetrahedron Letters 2004, 45, 8311-8313.
Substituted cyclohexadiene fullerenes have also been used for fundamental studies, see for example Liou et al., J. Chem. Soc., Chem. Commun. 1995, 1603-1604, An et al., J. Org. Chem. 1995, 60, 6353-6361, Cossu et al., J. Org. Chem. 1996, 61, 153-158, Hsiao et al., J. Am. Chem. Soc. 1998, 120, 12232-12236, Qian et al., J. Am. Chem. Soc. 2000, 122, 8333-8334, Inoue et al., Synlett 2000, 1178-1180, Iwamatsu et al., Org. Lett. 2002, 4, 1217-1220, and Vida et al., Macromol. Rapid Commun. 2007, 28, 1345-1349.
KR 1128833 B1 describes an organic/inorganic hybrid solar cell containing a fullerene derivative and a dye in an inorganic semiconductor, where the fullerene derivative, including one monosubstituted cyclohexadiene fullerene example, contains at least one of carboxylic acid group, anhydride group, phosphoric acid group, siloxane group, and sulfonic acid group. However, such groups have the drawback that they can act as charge traps in an OPV device configuration and liberate acidic protons (H+) that are detrimental for the performance and lifetime of the OPV device.
Until now monosubstituted or polysubstituted cyclohexadiene fullerenes as disclosed and claimed hereinafter have not been suggested as potential candidates to replace PCBM type fullerenes in the photoactive layer of a OPV or OPD device, or for use as p-type or n-type semiconductor in an OFET or OLED device.
For example, the data reported for the cyclohexadiene fullerenes that are functionalized with unsubstituted thiophene rings as disclosed in Vida et al., Macromol. Rapid Commun. 2007, 28, 1345-1349, do not suggest that these fullerene derivatives could be interesting candidates for OPV/OPD application, because relevant information for such a use, like the electron mobility, energetic level (particularly LUMO level) and solid state morphology have not been reported.